defiantly poa, I don't know about the field being permanently contaminated, re-sodding is the answer. There is a new product in its early stages called Mesotrione (Velocity), some people have had some success with it, but it is costly.

It looks like a Poa infestation that was spread by a triplex mowers rollers. See how the Poa stripes match the mowing stripes. This happens a lot on putting greens. Some golf courses have to wash their triplex's several times a mow just because of this.